The invention concerns a device to deoil the crankcase ventilation gases of an internal combustion engine with at least one oil mist separator which has a gas inlet that is connected to the crankcase, a gas outlet that is connected to the air intake section and an oil outlet that is connected to the oil sump of the internal combustion engine.
During the operation of an internal combustion engine so-called blow-by-gases get inside the crankcase and have to be drawn off since, otherwise, there would be an unwanted increase of internal pressure in the crankcase. To achieve this, the blow-by-gases are redirected to the air intake section as crankcase ventilation gases via an air vent channel. In order to deoil the crankcase ventilation gas the gases are directed in a known way through an oil mist separator, whose gas inlet is connected directly or indirectly via a crankcase low-pressure control valve to the crankcase and whose gas outlet is connected directly or indirectly via the crankcase low-pressure control valve to the air intake section. In this way, the oil mist separator generates a pressure difference (xcex94p=p1xe2x88x92p2) because of its flow resistance.
In the following description, the pressure area on the gas inlet side will be called the 1st pressure area (p1) and the pressure area on the gas outlet side will be called the 2nd pressure area (p2).
The differential pressure drop over the oil mist separator directly causes a rise in pressure in the crankcase. The degree of separation of the oil mist separator also depends on the pressure difference.
Preferably, cyclones or so-called coalescence separators in the form of a knitted separator or a wrap-round separator are used as oil mist separators. A cyclone oil mist separator, for example, is known from DE 14 324 C2. A deoiling device with a coalescence separator is described in DE 197 29 439 A1.
The problem with the use of an oil mist separator however is that its flow resistance and therefore the pressure difference generated by the oil mist separator is not constant but changes depending on the type of oil mist separator that is used in association with the specific parameters. In the case of a cyclone, the flow resistance and hence the generated pressure difference depends on the volumetric flow of the blow-by gases. This in turn depends on the load state and the rotational speed of the internal combustion engine, which can change in the short term. The volumetric flow of the blow-by gases is also dependent on the wear of the internal combustion engine, which increases over time. In the case of a knitted separator or a wrap-round separator the flow resistance depends on the degree of contamination, which can also increase over time. To remedy this, the known state of the art recommends a bypass channel controlled by a valve that adjusts to the differential pressure. The disadvantage is that the oil mist does not precipitate out of the gas that passes through the bypass channel.
Increases in differential pressure in the oil mist separator that go beyond a specific level cause an unacceptable pressure increase in the crankcase, which causes damage to the internal combustion engine especially when its effect extends over a long time, or it occurs frequently.
The task of the invention therefore is to develop a device to deoil the crankcase ventilation gases, which will cause the oil mist to precipitate and prevent the unacceptable pressure increase in the crankcase under all operating conditions.
This task is achieved through the distinguishing features of claim 1. The associated subclaims contain advantageous working designs and the further development of the invention.
According to the invention, the device, in respect of its flow-through rate, uses a controllable bypass channel, which is located as a bypass in parallel to the oil mist separator in the crankcase air-bleed duct. To this end, the bypass channel has a gas inlet that is connected directly or indirectly to the crankcase (1st pressure area) and a gas outlet that is connected directly or indirectly to the air intake section (2nd pressure area). In order to control the gas flow-through rate, the invention provides for a device that, depending on the differential pressure (xcex94p=p1xe2x88x92p2) between the two pressure areas, opens and closes the bypass channel to enable the crankcase ventilation gases to flow through constantly or gradually and also causes the oil to separate off when the bypass channel is open. The bypass channel, together with its control device, has been developed so that deoiling will also occur in the bypass channel as a result of flow diversion and impact separation or as a result of impaction. The separation behaviour of the entire device (oil mist separator plus controllable bypass channel) ensures that the level of separation is sufficiently high even when the bypass is open. To carry away the oil that has separated off in the bypass channel, the bypass channel is connected to the oil sump for example via an oil outlet.
If the differential pressure in the oil mist separator exceeds a specific value, the device releases the bypass channel for the crankcase ventilation gas to flow through so that a partial volumetric flow of the crankcase ventilation gas flows past the oil mist separator through the bypass channel into the 2nd pressure area (air intake section). In this way, a damaging rise in pressure in the crankcase and an insufficient oil mist separation can be avoided.
In practice, the oil mist separator is designed so that it exhibits a specific degree of separation for a specific volumetric flow, and a specific differential pressure drop is also implicit. When determining the operating point, care must be taken to ensure that the differential pressure plus, if necessary, a certain tolerance zone lies below the critical limit for the crankcase pressure.
If the volumetric flows of the blow-by gas become permanently higher over time as a result of wear, even if the operating conditions (load state, rotational speed) of the internal combustion engine remain the same, in the case of a cyclone oil mist separator, this would cause a drastic rise in differential pressure, which in turn would result in a damaging rise in pressure in the crankcase. This rise in differential pressure can only be counteracted by the controllable bypass. The device that opens and closes the bypass channel is designed so that the opening pressure is equal to the differential pressure plus, if necessary, an extra tolerance that is critical for the crankcase.
According to the invention, the controllable bypass works in the same way with a knitted separator or a wrap-round separator, which, if the volumetric flow remained the same, would generate a substantially increased differential pressure in the entire device as a result of contamination over time. With a knitted separator or a wrap-round separator in particular, the invention provides for a sensor that detects whether the bypass channel is open or not. If the bypass channel is open (valve in the open position), an optical or acoustic warning signal is generated for the operator of the internal combustion engine. This signal is an indication that the knitted separator or wrap-round separator has reached a specific degree of contamination. The operator can then react accordingly and change the knitted separator or wrap-round separator.
The effect of the controllable bypass channel to reduce the differential pressure does not of course arise only with differential pressure rises that occur after a certain time as a result of the wear of the internal combustion engine or contamination of the oil mist separator, but also with differential pressure rises that occur in the short term.